Heating systems may be used in subterranean environments for various purposes. In one application, a subterranean heating system may be used to facilitate oil production. Oil production rates have decreased in many of the world's oil reserves due to difficulties in extracting the heavy oil that remains in the formation. Various production-limiting issues may be confronted when oil is extracted from heavy oil field reservoirs. For example, the high viscosity of the oil may cause low-flow conditions. In oil containing high-paraffin, paraffin may precipitate out and form deposits on the production tube walls, thereby choking the flow as the oil is pumped. In high gas-cut oil wells, gas expansion may occur as the oil is brought to the surface, causing hydrate formation, which significantly lowers the oil temperature and thus the flow.
Heating the oil is one way to address these common production-limiting issues and to promote enhanced oil recovery (EOR). Both steam and electrical heaters have been used as a source of heat to promote EOR. One technique, referred to as heat tracing, includes the use of mechanical and/or electrical components placed on piping systems to maintain the system at a predetermined temperature. Steam may be circulated through tubes, or electrical components may be placed on the pipes to heat the oil.
These techniques have some drawbacks. Steam injection systems may be encumbered by inefficient energy use, maintenance problems, environmental constraints, and an inability to provide accurate and repeatable temperature control. Although electrical heating is generally considered to be advantageous over steam injection heating, electrical heating systems typically cause unnecessary heating in regions that do not require heating to facilitate oil flow. The unnecessary heating is associated with inefficient power usage and may also cause environmental issues such as undesirable thawing of permafrost in arctic locations.
Accordingly, there is a need for a subterranean electro-thermal heating system that is capable of efficiently and reliably delivering thermal input to localized areas in a subterranean environment.